1. Field of the Invention
The present invention relates generally to defective preforms and more particularly to removal of defective preforms from an injection molding apparatus.
2. Related Art
Preforms created in the injection molding process are sometimes defective in that they cannot be easily removed from the core of the injection molding apparatus over which the preforms are shaped. One common example is when the plastic does not form the entire preform. In this instance the preform does not cover the core and cannot be removed from the core using the mold ejector plate. As a result, the defective preform must be cooled and struck at its bottom end with a hammer, such as a brass or aluminum hammer in order to crack the plastic and remove the preform from the core.
Most cores are made from steel and have sufficient hardness to withstand the impact of being struck with a hammer. The benefit of an ampcoloy core is that it decreases cycle times of molds by allowing the plastic to cool faster. However, ampcoloy cores are softer than steel and are very susceptible to damage when struck with a hammer. Using a hammer to remove a defective preform creates a likelihood that the core will bend when struck. A bent core cannot be straightened, so it must be replaced at significant cost.
Thus there is a need in the art for a mechanism for removal of defective preforms from the core of an injection molding apparatus which does not risk damaging the core.
One difficulty in using a brass hammer, regardless of the core with which it is used, it that the defective preform must be struck with just the right force. This may require multiple attempts. There is also a chance that the plastic will shatter, making clean-up tedious, time consuming, and potentially dangerous. Further, the process requires the use of man-power, which increases costs. The longer it takes to remove and clear a defective preform, the less time the molding apparatus is in use. This loss of time results in lower productivity, and ultimately, a reduction in efficiency.
Another device known in the art is a platen, which is a plate with a series of holes, corresponding to the location of the cores upon which the preforms are molded. To remove a defective preform, the large platen must be placed over all the cores that are in the assembly, adjusted to fit the cores tightly, and then the platen is forcefully pulled down to remove the defective preform. The problem with this method is that is requires alignment of the platen with multiple cores, the platen is large and cumbersome, and if the platen is not pulled down at the proper angle, the ampcoloy core can bend. Furthermore, platens are heavy, and require the use of an additional machine to put the platen into place and to remove it.
Thus there is also a need for a removal device and method of removal of individual defective preforms that is time efficient and requires minimal manual operation.